1. Field of the Invention
The present invention relates to an image forming apparatus that forms an image on a sheet to be supplied and, more particularly, to control of the drive speed of an intermediate feeding roller that feeds a sheet to a regist roller.
2. Description of the Related Art
In an image forming apparatus, an intermediate feeding roller that feeds a sheet to a regist roller (roller that performs skew correction or timing adjustment for a sheet being fed) has roles of performing sheet feeding operation at the time when an image is formed onto the sheet in cooperation with the regist roller and receiving a sheet supplied from a sheet supply cassette or sheet, onto the first surface of which an image has already been formed, fed for image forming on the second surface thereof (fed for duplex printing).
It is preferable that the sheet feeding speed of the intermediate feeding roller having the above roles be synchronized with the sheet feeding speed of a feeding roller or regist roller which is a partner for the sheet feeding operation. The sheet feeding speed with which the intermediate feeding roller should be synchronized includes a sheet supply speed (speed at which a sheet supplied from the cassette is fed to the regist roller), a process speed (sheet feeding speed when a sheet is fed through the regist roller at the time of toner image forming), and an ADU speed (feeding speed of a sheet to be resupplied for image forming onto the second surface thereof).
As a method for allowing the intermediate feeding roller to realize a plurality of different sheet feeding speeds, one in which a pulse motor is used a lot for the drive of feeding rollers that perform sheet feeding in an apparatus and one in which a plurality of clutch mechanisms are used for them can be taken. However, these methods may increase cost.
Further, even in the configuration in which the clutch mechanism is adopted to drive the intermediate feeding roller, only two different sheet feeding speeds have been realized so far (refer to, for example, Jpn. Pat. Appln. Laid-Open Publication No. 2001-130811).
In recent years, in order to increase sheet feeding efficiency, intervals between sheets tend to be short in the sheet feeding operation in which a plurality of sheets are sequentially fed. It is difficult to perform connection or stop of the clutch mechanism at a fraction of the time while performing the sequential sheet feeding operation with short sheet interval as described above. Further, misalignment in the feeding speed at the time of delivery and receipt of the sheet between rollers or the like may cause roller surface wear and sheet jamming.